Importance of non-intrinsic platinum dissolution in Pt/C composite fuel cell catalysts.

Primož Jovanovič,Vid Simon Šelih,Nejc Hodnik,Francisco Ruiz-Zepeda,Miran Gaberšček,Martin Šala,Urša Petek,Matija Gatalo,Tim Patrick Fellinger

doi:10.1039/c7cp03192k

Abstract

The dissolution of different platinum-based nanoparticles deposited on a commercial high-surface area carbon (HSAC) support in thin catalyst films is investigated using a highly sensitive electrochemical flow cell (EFC) coupled to an inductively coupled plasma mass spectrometer (ICP-MS). The previously reported particle-size-dependent dissolution of Pt is confirmed on selected industrial samples with a mean Pt particle size ranging from 1 to 4.8 nm. This trend is significantly altered when a catalyst is diluted by the addition of HSAC. This indicates that the intrinsic dissolution properties are masked by local oversaturation phenomena, the so-called confinement effect. Furthermore, by replacing the standard HSAC support with a support having an order of magnitude higher specific surface area (a micro- and mesoporous nitrogen-doped high surface area carbon, HSANDC), Pt dissolution is reduced even further. This is due to the so-called non-intrinsic confinement and entrapment effects of the (large amount of) micropores and small mesopores doped with N atoms. The observed more effective Pt re-deposition is presumably induced by local Pt oversaturation and the presence of nitrogen nucleation sites. Overall, our study demonstrates the high importance and beneficial effects of porosity, loading and N doping of the carbon support on the Pt stability in the catalyst layer.

Highlights

New strategies to study the catalyst layers have been developed
Visualization of the catalyst layer has been addressed by coupling electrochemical tools with other high resolution methods, mostly by ex situ approaches such as identical location transmission electron microscopy (IL-TEM)[14,15,16,17,18] and identical location scanning electron microscopy (IL-SEM).[19,20,21]
We use the same analytical tool on a novel, highly-porous nitrogen doped carbon Pt composite (Pt@HSANDC) and demonstrate the stabilizing effect of the high surface area carbon support with large amounts of micro- and small mesopores doped with N atoms on the dissolution of Pt nanoparticles

Summary

Introduction

New strategies to study the catalyst layers have been developed. In large part, these strategies rely on a combinatorial approach where new analytical concepts have provided novel insights into the dissolution of platinum or more general catalyst layer degradation mechanisms.[5,6,7,8,9,10,11,12] In situ experimental methodologies are especially insightful, where the electrochemical treatment of the catalyst layer is coupled with one or several highly sensitive analytical tools (e.g. X-ray absorption spectrometers, XRD diffractometers and mass spectrometers). Some studies involving N-doped carbon supports only showed an increased initial activity but no particular improvement in catalyst stability.[31] Even though performed in a simple half-cell configuration, these studies shed new light on the extensive complexity of the catalyst composite dissolution process This calls for further investigation before real catalyst layers should be designed. We use the same analytical tool on a novel, highly-porous nitrogen doped carbon Pt composite (Pt@HSANDC) and demonstrate the stabilizing effect of the high surface area carbon support with large amounts of micro- and small mesopores doped with N atoms on the dissolution of Pt nanoparticles

Electrochemical flow cell coupled to ICP-MS

Results and discussion

Conclusion